1. Field of Invention
The field of the currently claimed embodiments of this invention relates to systems, devices and methods for cochlear implant surgery.
2. Discussion of Related Art
Many different types of Cochlear implant surgery (J. Niparko (ed), Cochlear Implants: Principles & Practices, Philadelphia, Lippincott, Williams & Wilkins, 2009; D. Tucci and T, Pilkington, “Medical and surgical aspects of cochlear implantation”. in Cochlear Implants: Principles & Practices, J. K. Niparko, Ed, Philadelphia: Lippincott, Williams & Wilkins, 2009) can be of immense auditory, linguistic and developmental benefit to patients with severe hearing loss due to the loss of hair cell transduction within the cochlea. Estimates from the National Institute of Deafness and Other Communication Disorders (NIDCD) are that approximately 188,000 people worldwide have received implants (“Statistics about Hearing, Balance, Ear Infections, and Deafness,” http://wwvv.nidcd.nih.gov/health/statistics/hearing.asp#1,2010) and that rates of applying electrified implants to the ear are accelerating.
The surgical procedure is potentially complicated by difficulties with implant electrode array insertion (e.g., C. J, Coulson, A. P. Reid, D. W. Proops, and P. N. Brett, “ENT challenges at the small scale”, Int J Med Robot, vol. 3-2, pp. 91-6, June 2007. http://www.ncbi.nlm,n1h,gov/entrez/query fcgi?cmd=Retrieve&db=PubMed& dopt=Citation&list uids=17619240 10.1002/rcs.132) and serious complications may occur. One particularly challenging step is the actual insertion of the implant into the cochlea (see, e.g., FIGS. 1A-1C). After accessing the scala tympani (via direct round window insertion, or drilling open a cochleostomy to gain access to the cochlea) an electrode array is inserted into scala tympani of the cochlea. Several designs of cochlear implant arrays have relied on stylet-based insertion techniques. The Advanced Bionics arrays used in ca. 2003-2006 used a pre-curved array that was loaded onto a hand-held insertion tool. Once inserted into the scala tympani, the insertion tool was used to guide the array into the proximal 3 mm of the scala and then advance the array off of the rigid stylet into the first turn of the cochlea, allowing the curvature of the silastic carrier to find the proper trajectory through the turn. Here, if the stylet based on the hand-held tool were to be advanced too far into the cochlea, contact forces generated can damage the cochlea.
Over the past 6 years, the Cochlear Corporation Freedom and C512 arrays have used a stylet-based strategy: A stylet is used to hold the implant straight while it is inserted to a desired depth into the cochlea. The array is advanced over the stylet, which is held in a fixed position. The implant array then naturally curves to follow the cochlea given it's memory as a curved array once off of the stylet. The stylet is then withdrawn. If the stylet and implant are advanced too far into the cochlea, the resulting contact forces can damage the cochlea either due to direct impact or buckling of more proximal aspects of the carrier. Research also has been reported in which a sheath-style insertion device is used to perform the same function as a stylet in holding the implant straight while it is inserted to a desired depth into the cochlea. The implant array naturally curves to follow the cochlea as it is deployed further through the sheath. One example of such a sheath is the Modiolar Research Array (R. Briggs et al., “Development and evaluation of the modiolar research array—multi-centre collaborative study in human temporal bones”, Cochlear Implants Int. 2011 August 12(3) pp 129-139, PMCID: PMC3159433). Again, if the stylet and implant are advanced too far into the cochlea, the resulting contact forces can damage the cochlea either due to direct impact or buckling of more proximal aspects of the carrier.
Many other array designs used both historically and presently present a potential problem with substantial growth in resistance as the array is inserted beyond 12 mm (Tucci, et al.), with consequent risks to the integrity of intracochlear membranous structures (FIG. 2).
Several approaches to providing guidance or assistance in avoiding damage to the cochlea during implant insertion have been reported recently. Labadie et al. report a microstereotactic device for aligning an implant array with the cochlea for percutaneous insertion based on preoperative images (R. F. Labadie, R. Balachandran, J. Mitchell, J. H. Noble, O. Majdani, D. Haynes, M. Bennett, B. M. Dawant, and M. Fitzpatrick, “Clinical Validation Study of Percutaneous Cochlear Access Using Patient Customized Micro-Stereotactic Frames”, Otol. Neurotol, vol. 31-1, pp. 94-99, 2010, PMC2845321). Schurzig, Labadie, and Webster report a system that combines an “active canula” robot with delicate force sensing capabilities to sense contact between the implant and the cochlea (D. Schurzig, R. F. Labadie, and R. J. Webster, “A force sensing robot for cochlear electrode implantation”, in IEEE International Conference on Robotics and Automation, 2010, pp. 3674-3679), using a force sensor incorporated into the robotic mechanism that advances the implant into the cochlea, Rau et al. (T. S. Rau, A. Hussong, M. Leinung, T. Lenarz, and O. Majdani, “Automated insertion of preformed cochlear implant electrodes: evaluation of curling behaviour and insertion forces on an artificial cochlear model”, Int Comput Assist Radio! Surg, vol. 5-2, pp. 173-81, March 2010.http://www,ncbi,nlm.nih'govientrez/query. fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list uids=20033522 10,1007/s11548-009-0299-9) have also proposed a robotic cochlear insertion device and have reported phantom studies of insertion forces using a load cell attached to the insertion mechanism. Zhang, Simaan, et al. have developed an actively deforming, steerable, cochlear implant that curves to follow the cochlea during insertion (J. Zhang, W. Wei, S, Manolidis, J. T. Roland, Jr., and N. Simaan, “Path planning and workspace determination for robot-assisted insertion of steerable electrode arrays for cochlear implant surgery”, Med Image Comput Comput Assist Interv, vol. 11-Pt 2, pp. 692-700, 2008.http://www.ncbi,nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed & dopt=Citation&list uids=18982665; J. Zhang, K, Xu, N. Simaan, and S. Manolidis, “A pilot study of robot-assisted cochlear implant surgery using steerable electrode arrays”, Med Image Comput Comput Assist Interv, vol. 9-Pt 1, pp. 33-40, 2006. http://www.ncbi.nlm,nih.zov/entrez/querylegi?cmd=Retrieve&db=PubMed& dopt=Citation&list uids=17354871; J. Zhang, W. Wei, J. Ding, J. T. Roland, S. Manolidis, and N. Simaan, “Inroads Toward Robot-Assisted Cochlear Implant Surgery Using Steerable Electrode Arrays”, Otology and Neurotology, p. in Press; Published ahead of print, 2010 10.1097/MA0.0b013e3181e7117e). They report experiments using a load cell mounted on their robotic manipulation device. Some limitations of these systems include reliance on a fairly large and cumbersome robotic insertion tool and the necessity to implement an extremely delicate force sensing mechanism. In the case of the reported systems, the difficulty is exacerbated by the moving mass of the mechanism distal to the force sensor and possible friction forces.
Other authors (e.g., C. J. Coulson, R. P. Taylor, A. P. Reid, M, V. Griffiths, D. W. Proops, and P. N. Brett, “An autonomous surgical robot for drilling a cochleostomy: preliminary porcine trial”, Clin Otolaryngol, vol. 33-4, pp. 343-7, August 2008. http://www.ncbi,n1m.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed& dopt=Citation&list uids=18983344C0A1703 [pii] 10.1111/j.1749-4486.2008.01703.x; O. Majdani, D, Schurzig, A. Hussong, T. Rau, I. Wittkopf, T. Lenarz, and R. F. Labadie, “Force measurement of insertion of cochlear implant electrode arrays in vitro: comparison of surgeon to automated insertion tool”, Acta Oto-Laryngologica, vol. 130-1, pp. 31-36, January 2010. <Go to ISI>://000274416300005Doi 10.3109/00016480902998281) have proposed robotic devices to assist in drilling the skull to gain access to the cochlea for implant insertion. These systems do not address the problem of inserting an implant without damage to the cochlea.
Skilled otologic surgeons have the manual dexterity and steadiness to insert implants without damage to the cochlea. What they lack is feedback to know when the implant or stylet has been introduced too far into the cochlea. In his review article (C. J, Coulson, et al, id), C. J. Coulson states:                If the surgeon were able to visualize or ‘feel’ forces imparted on the electrode array and then guide the array around the path of least resistance, he/she would be able to place the electrode whilst minimizing the trauma to the cochlea.        
Coulson further suggests an endoscopic “flexible digit with visualization (the scala tympani being about 1 mm2 in cross-section) would allow the tip to be manoeuvred through the hollow portion of the scala tympani”, but discloses no feasible way to implement such a device, which he describes as being “technically very difficult” since it would require both a light source and a visualization device in a tiny space. As an alternative, he suggests:                Another potential solution would be to fit the electrode array with sensing elements at the tip, which could feed back onto a monitor, informing the surgeon whether the tip was against the solid outer cochlear wall or in the middle of the hollow scalatympani.        
However, he does not disclose any feasible means for performing such sensing and implies that he is interested only in contact/noncontact sensing. Some implant manufacturers (e.g., Cochlear Corp) place fiducial marks along the implant to assist the surgeon in determining how deep the implant has been inserted into the cochlea and, hence, how much further it can be inserted before it comes into contact with the cochlear wall at the start of the “turn” into the high curvature portion of the cochlea. One limitation of this approach is that the surgeon has no clearly defined reference for relating the fiducial marks to the highly variable position of the opening in the cochlea. Similarly, the surgeon lacks a patient-specific measurement giving the exact depth of insertion required. There thus remains a need for improved systems, devices and methods for cochlear implant surgery.